7c: Client data cache management via element attributes
(sx-cache-invalidate) and response headers (SX-Cache-Invalidate,
SX-Cache-Update). Programmatic API: invalidate-page-cache,
invalidate-all-page-cache, update-page-cache.
7d: Service Worker (sx-sw.js) with IndexedDB for offline-capable
data caching. Network-first for /sx/data/ and /sx/io/, stale-while-
revalidate for /static/. Cache invalidation propagates from
in-memory cache to SW via postMessage.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>